#include <iostream>

int main()
{
    std::cout << "Hello, world!" << std::endl;
    return 0;
}

Compile and run:

g++ main.cpp -o main
./main

This is the smallest C++ program shape: main starts the program, and std::cout prints to the terminal.

#include <string>

std::string name = "Dan";
int count = 1;
bool active = true;
auto language = "C++";

This shows a few common C++ value types and auto for type inference when the initializer already makes the type obvious.

#include <string>

std::string greet(const std::string& name)
{
    return "Hello, " + name + "!";
}

This defines a function that takes a name and returns a greeting string. It is the usual pattern for reusable logic in C++.